code423n4 commented 2 years ago

C4-001 : ++i is more gas efficient than i++

Impact

++i is more gas efficient than i++ in loops forwarding.

Proof of Concept

Navigate to the following contracts.

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L116

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L110

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L125

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/Swapper.sol#L14

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/DiamondLoupeFacet.sol#L24

Tools Used

Code Review

Recommended Mitigation Steps

It is recommend to use unchecked{++i} and change i declaration to uint256.

C4-002 : Cache array length in for loops can save gas

Impact

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Proof of Concept

Navigate to the following smart contract line.

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L116

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L110

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L125

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/Swapper.sol#L14

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/DiamondLoupeFacet.sol#L24

Tools Used

None

Recommended Mitigation Steps

Consider to cache array length.

C4-003 : `> 0 can be replaced with != 0 for gas optimization`

Impact - Gas Optimization

!= 0 is a cheaper operation compared to > 0, when dealing with uint.

Proof of Concept

Navigate to the following contract function and lines.

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/NXTPFacet.sol#L98

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/HopFacet.sol#L109

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/AnyswapFacet.sol#L92

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/AnyswapFacet.sol#L105

Tools Used

Code Review

Recommended Mitigation Steps

Use "!=0" instead of ">0" for the gas optimization.

C4-004 : `Use short reason strings can save gas`

Impact

Shortening revert strings to fit in 32 bytes will decrease deploy time gas and will decrease runtime gas when the revert condition has been met.

Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Proof of Concept

Revert strings > 32 bytes are here:

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L113

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L154

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L156

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L187

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L189

Tools Used

Manual Review

Recommended Mitigation Steps

Shorten the revert strings to fit in 32 bytes. That will affect gas optimization.

C4-005 : Adding unchecked directive can save gas

Impact

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

Proof of Concept

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L116

Tools Used

None

Recommended Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible.

C4-006 : Free gas savings for using solidity 0.8.10+

Impact

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

Proof of Concept

Solidity 0.8.10 has a useful change which reduced gas costs of external calls which expect a return value: https://blog.soliditylang.org/2021/11/09/solidity-0.8.10-release-announcement/

Code Generator: Skip existence check for external contract if return data is expected. In this case, the ABI decoder will revert if the contract does not exist

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.10.

C4-007 : Check if amount > 0 before token transfer can save gas

Impact

Since _amount can be 0. Checking if (_amount != 0) before the transfer can potentially save an external call and the unnecessary gas cost of a 0 token transfer.

Proof of Concept

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/HopFacet.sol#L67

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider checking amount != 0.

C4-008 : Use `calldata` instead of `memory` for function parameters

Impact

In some cases, having function arguments in calldata instead of memory is more optimal.

Consider the following generic example:

contract C {
function add(uint[] memory arr) external returns (uint sum) {
uint length = arr.length;
for (uint i = 0; i < arr.length; i++) {
sum += arr[i];
}
}
}

In the above example, the dynamic array arr has the storage location memory. When the function gets called externally, the array values are kept in calldata and copied to memory during ABI decoding (using the opcode calldataload and mstore). And during the for loop, arr[i] accesses the value in memory using a mload. However, for the above example this is inefficient. Consider the following snippet instead:

contract C {
function add(uint[] calldata arr) external returns (uint sum) {
uint length = arr.length;
for (uint i = 0; i < arr.length; i++) {
sum += arr[i];
}
}
}

In the above snippet, instead of going via memory, the value is directly read from calldata using calldataload. That is, there are no intermediate memory operations that carries this value.

Gas savings: In the former example, the ABI decoding begins with copying value from calldata to memory in a for loop. Each iteration would cost at least 60 gas. In the latter example, this can be completely avoided. This will also reduce the number of instructions and therefore reduces the deploy time cost of the contract.

In short, use calldata instead of memory if the function argument is only read.

Note that in older Solidity versions, changing some function arguments from memory to calldata may cause "unimplemented feature error". This can be avoided by using a newer (0.8.*) Solidity compiler.

Examples Note: The following pattern is prevalent in the codebase:

function f(bytes memory data) external {
(...) = abi.decode(data, (..., types, ...));
}

Here, changing to bytes calldata will decrease the gas. The total savings for this change across all such uses would be quite significant.

Proof Of Concept

Examples:

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L116

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L110

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L125

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/Swapper.sol#L14

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/DiamondLoupeFacet.sol#L24

Tools Used

None

Recommended Mitigation Steps

Change memory definition with calldata.

C4-009 : Use of constant keccak variables results in extra hashing (and so gas)

Impact

That would Increase gas costs on all privileged operations.

Proof of Concept

The following role variables are marked as constant.

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Libraries/LibDiamond.sol#L7

This results in the keccak operation being performed whenever the variable is used, increasing gas costs relative to just storing the output hash. Changing to immutable will only perform hashing on contract deployment which will save gas.

See: ethereum/solidity#9232 (https://github.com/ethereum/solidity/issues/9232#issuecomment-646131646)

Tools Used

Code Review

Recommended Mitigation Steps

Consider to change the variable to be immutable rather than constant.

C4-010 : Changing function visibility from public to external can save gas

Impact

There is a function declared as public that are never called internally within the contract. It is best practice to mark such functions as external instead, as this saves gas (especially in the case where the function takes arguments, as external functions can read arguments directly from calldata instead of having to allocate memory).

Proof of Concept

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/WithdrawFacet.sol#L20

Tools Used

Code Review

Recommended Mitigation Steps

All of the public functions in the contract are not called internally, so access can be changed to external to reduce gas.

C4-011 : Non-strict inequalities are cheaper than strict ones

Impact

Strict inequalities add a check of non equality which costs around 3 gas.

Proof of Concept


All Facets Directory Contracts
Examples : 
https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/HopFacet.sol#L67

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/HopFacet.sol#L67

https://github.com/code-423n4/2022-03-lifinance/blob/main/src/Facets/CBridgeFacet.sol#L105

Tools Used

Code Review